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onLoad & onChange

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In this lesson, you will learn:

  • When onLoad and onChange scripts run
  • The parameters of an onChange script
  • Why the isLoading check matters

1 Two most common types

Most client scripts are onLoad or onChange. One runs when the form opens. The other runs when a field changes. 🔄

A timeline of client scripts on a form. First, the form opens and onLoad scripts run. onChange scripts also run once during loading, with isLoading set to true. Then the user changes Category from Software to Network, and the onChange script for Category runs with oldValue software, newValue network, and isLoading false.
Figure 1. onLoad runs once when the form opens. onChange runs whenever its field changes.

2 onLoad

An onLoad script runs when the form opens, before the user can type. Use it to set up the form.

function onLoad() {
  if (g_form.isNewRecord()) {
    g_form.addInfoMessage('Tip: pick a Category first.');
  }
}

💡 Good to know: Keep onLoad scripts short. Every onLoad script makes the form a little slower to open.

3 onChange

An onChange script watches one field (set in Field name). It runs when that field’s value changes.

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
  if (isLoading || newValue === '') {
    return;   // do nothing while the form loads, or if cleared
  }
  if (newValue == 'network') {
    g_form.setValue('impact', '2');
    g_form.showFieldMsg('category', 'Impact set to Medium.', 'info');
  }
}
Parameter What it holds
control The field’s HTML element (rarely used)
oldValue The value when the form loaded
newValue The new value
isLoading true while the form is still loading
isTemplate true if a template changed the value

⚠️ Heads up: onChange scripts also run once while the form loads. Without the isLoading check, your script might change values every time someone just opens a record!

⭐ Remember: onLoad = form opens. onChange = one field changes. Always start onChange with if (isLoading || newValue === '') return;

4 Let’s try it: Network means Medium impact

  1. Create a client script. Name: SNWR network impact. Table: Incident. Type: onChange. Field name: Category.
  2. Paste the onChange example above. Submit.
  3. Open a new incident. Set Category to Network. Did Impact change to 2 – Medium?
  4. Save it, then reopen it. Does the message show up again? (It shouldn’t, thanks to isLoading.)

5 Quick recap

  • onLoad runs once when the form opens
  • onChange runs when one chosen field changes
  • onChange gets oldValue, newValue, and isLoading
  • Check isLoading so your script doesn’t run on load by mistake

6 Check yourself

Think of your answer first. Then tap to check.

1 Which type would you use to show a tip when a new form opens? Show answer

onLoad.

2 Where do you choose which field an onChange script watches? Show answer

The Field name field on the client script.

3 Why check isLoading in an onChange script? Show answer

onChange also runs while the form loads. The check stops it from acting when nobody changed anything.

Nice work! You finished this lesson. 🎉

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